(Not Applicable)
(Not Applicable)
The present invention generally relates to solid state laser systems, and more particularly to a laser system that uses high temperature laser diodes as an optical pumping source.
Solid-state laser systems have been recognized as an efficient method of producing laser light. In such systems, atoms present in a crystalline or glass host material or medium absorb light produced by an external pump source and thereby achieve an excited state to generate light at a known wavelength. The host laser medium is mounted in an optical cavity which provides the optical feedback necessary for proper laser action. The result is a simple and versatile laser which has become a standard tool for diverse applications.
The choice of the optical pump source (external light) to excite the laser medium strongly influences laser characteristics. The optical pump source can be chosen from a pulsed flash lamp, a continuous arc lamp or a semiconductor (diode) laser. Both flash lamp and continuous arc lamp pumping tend to be electrically inefficient and create significant amounts of waste heat since the spectral range of the lamp is much broader than the absorption range of the laser medium. Only a small portion of the light from these types of pump sources is absorbed by the laser medium, thereby creating an inefficient laser system.
On the other hand, laser diodes have been recognized as providing an efficient pump source in solid-state laser systems since the 1960""s. When employed as a pump source, the laser diode is used to generate light which overlaps the spectral band of the laser medium. Optimally, the laser diode generates light in a narrow spectral regime that overlaps the primary absorption band of the laser medium, with the wavelength of the light generated by the laser diode being matched to the absorption region of the host laser medium. The laser diode is considered to be more efficient as a pump source than a flash lamp or an arc lamp since the light produced by the laser diode is more closely matched to the host laser medium.
Though providing advantages over alternative types of pump sources, the use of a laser diode as an optical pump source give rise to certain difficulties, most of which are attributable to the requirement to maintain precise thermal control of the laser diode for its proper operation. In those laser systems in which laser diodes have been employed, the laser diodes comprise continuous wave (CW) laser diodes which are operative to emit light at about 810 nm at ambient or room temperature. The proper operation of these laser diodes requires the precise thermal control thereof to maintain the temperature of the same at room temperature. Indeed, the wavelength of light produced by these laser diodes can shift at a rate of about 1 nm for every shift in temperature of 3xc2x0 C. As a result, in order to maintain the operating temperature of these laser diodes at room temperature, those laser systems incorporating the same must be provided with components or systems such as thermal electric controllers, heat spreaders, and/or heat sinks for purposes of dissipating the heat generated by the operation of the laser diode(s). As will be recognized, if such generated heat is not fully dissipated, the resultant temperature increase within the laser diode(s) will result in the same emitting longer wavelengths of light which will not be optimally matched to the absorption region of the laser medium of the laser system.
As indicated above, in those prior art laser systems which include one or more laser diodes as the optical pump source, such laser diodes are adapted to optimally operate at room temperature. As a result, these prior art laser systems rely upon the inclusion of thermal electric cooling with large heat sinks and/or water cooling to maintain the room temperature operating conditions required by the laser diode(s) thereof. Also used in some of these prior art systems are silicon micro-channel coolers with low thermal impedance which are operative to extract heat from the laser diode junction(s). However, the need to provide the prior art laser systems with these and other types of cooling systems provides significant disadvantages due to such cooling systems requiring excessive amounts of energy to operate, typically being large in size, and further being complex in construction and therefore prone to failure.
There has recently been developed laser diodes that are specifically configured to operate at temperatures above room temperature, and more particularly at temperatures of at least about 70xc2x0 C. These laser diodes are operable to generate light at a wavelength in the range of from about 800 to 812 nm at temperatures above 70xc2x0 C. As such, in order for these high-temperature laser diodes to operate properly, they must necessarily be heated to a temperature level above ambient or room temperature. Indeed, the heat produced by these laser diodes as a result of their normal operation actually contributes to their ability to generate light of a precise wavelength. Thus, not only do such laser diodes typically not require extensive cooling for their proper operation, they actually must be heated to above room temperature for their proper operation to occur.
In the present invention, Applicant has recognized that many of the disadvantages present in prior art laser systems including laser diodes which must be maintained at room temperature could be eliminated if such laser diodes were to be replaced with those which are specifically suited to operate at elevated temperatures. In this respect, Applicant also recognized that in such a laser system, the need to include complex cooling systems or units would be avoided due to the high temperature operational thresholds of the laser diodes included therein. As such, the present invention provides a laser system which is capable of operating at elevated temperatures reliably without the need for or the inclusion of a complex cooling system for the laser diodes of the laser system.
In accordance with the present invention, there is provided a laser system which is particularly suited to operate at elevated temperatures, thus eliminating the need to integrate an extensive cooling system thereinto. The laser system of the present invention comprises a laser media which defines first and second optical ends and an input port. In a preferred embodiment of the present invention, the laser media comprises a Nd:YAG laser media, though the same may alternatively comprise a Nd:YLF laser media. In addition to the laser media, the laser system includes a pair of identically configured, high-temperature laser diodes which are in optical communication with the laser media and operative to collectively generate a source beam of light which is transmitted into the input port of the laser media. Importantly, the laser diodes are specifically adapted to operate at a temperature of at least about 70xc2x0 C., and to generate the source beam at a wavelength in the range of from about 800 nm to about 812 nm when in their optimal operating temperature range. Additionally, the laser diodes may be configured to operate in either a continuous wave mode or a pulse mode.
In addition to the laser media and laser diodes, the present laser system includes at least one reflector which is in optical communication with the first optical end of the laser media, and at least one optical coupler which is itself in optical communication with the second optical end of the laser media. The laser system may also include a Q-switch, such as an acoustic-optical modulator, which is in optical communication with the optical coupler. The laser media, the reflector and the optical coupler are configured to form a laser resonator operative to generate a laser beam which is transmitted through the optical coupler.
In addition to the above-described components, the present laser system preferably comprises a heater which is in conductive communication with the laser diodes for selectively heating the same to their minimum threshold of their prescribed operating temperature range. More particularly, when necessary, the heater facilitates the heating of the laser diodes to an operating temperature of at least about 70xc2x0 C. which is required for the proper operation of the laser diodes. The heating of the laser diodes by the heater will typically occur upon the start-up of the laser system to elevate the temperature of the laser diodes to the required level. Additionally, the heater will sometimes be employed when the operating temperature of the laser diodes may fall below the 70xc2x0 C. threshold as could occur when they are operated in a pulse mode. However, the natural tendency of the laser diodes to generate heat as a result of their normal operation is instrumental in maintaining the operating temperatures thereof at or at least close to the minimum threshold or level of about 70xc2x0 C.
Though the laser diodes are configured to operate at a temperature of at least about 70xc2x0 C., the proper operation of such diodes requires that the temperatures thereof do not exceed about 80xc2x0 C. In those instances when the temperatures of the laser diodes may exceed 80xc2x0 C. due to the operation thereof in a continuous wave mode, the laser system of the present invention is preferably provided with a simple cooling unit such as a fan which, when activated, is operative to reduce the temperature levels of the laser diodes to within their the preferred operating temperature range of from about 70xc2x0 C. to about 80xc2x0 C. Because the laser diodes in the present laser system are particularly suited to operate at elevated temperatures, and need only be cooled under limited circumstances, the need to include a complex cooling system or unit in the present laser system is avoided. Since known cooling systems are typically large in size, of substantial weight, require substantial energy, and are prone to failure, the elimination thereof from within the present laser system provides significant advantages in size reduction and operational efficiency.
Further in accordance with the present invention, there is provided a method of producing a laser beam through the use of a laser system which is capable of operating at high temperatures with minimal cooling requirements. The method comprises the initial step of producing a source beam of light through the use of at least one laser diode having a prescribed minimum operating temperature of at least about 70xc2x0 C. The source beam of light is then transmitted into a laser media to produce a second beam which is itself reflected through the laser media via a reflector and an optical coupler to generate an output beam. The source beam of light may be produced via a pair of laser diodes, and in either a continuous wave mode or a pulse wave mode. As indicated above, the source beam of light is preferably produced so as to have a wavelength in the range of from about 800 to 812 nm.